For the above silicon single-crystal layer, it is possible to name a silicon wafer which is produces by modifying an ingot of a silicon single-crystal which is grown during a pulling operation according to a CZ (Czochralski method) or a silicon single-crystal which is formed by an Epitaxial growing method on a base board.
A device is formed by forming a thin oxide film on a surface of such a silicon single-crystal layer and layering various substrates thereon by a photolithography step and an etching step, etc., in a predetermined pattern.
Here, a fine defect which is caused by a modifying operation in a production process on a surface of the silicon single-crystal layer of a silicon wafer which has been used conventionally. Such a fine defect is a damage which is caused by, for example, a machine operation such as a grinding processing operation, an incompleteness or singular point, etc which is caused by a chemical operation by a metal element in a chemical liquid.
An inventor of the present invention found a fact in that, if a cleaning operation or an etching operation is performed to a surface of the silicon single-crystal layer which has such a defect, a defect which remains on the surface is elicit; thus, a reliability (GOI: Gate Oxide Integrity) of the oxide film which is formed on the surface is reduced.
It is anticipated due to that a cleaning liquid and an etchant work on a weak region on a surface of the silicon single-crystal layer collectively; thus, such a phenomenon is evident in a case in which a member such as a hydrofluoric acid is used for the cleaning liquid and the etchant which are preferably selected.
There was a case in which a quality of a device which is formed on a surface of the silicon single-crystal layer is defective and the product yield is worsened if the silicon single-crystal layer is formed when the GOI of the silicon single-crystal layer is deteriorated by using such a cleaning liquid and the etchant.
Conventionally, there have been proposed several methods for improving a quality of a surface of the silicon single-crystal layer to which the thermal processing operation is performed in advance. For example, in a patent document 1 which is explained hereafter, an annealing processing operation it is disclosed for reducing a COP (Crystal Originated Particle) which is a defect which is caused by a crystal by performing a thermal processing operation such as an RTA processing operation for 1 to 60 seconds at a temperature 1150° C. to 1300° C. in a hydrogen gas or an argon gas atmosphere.
Also, in a patent document 2 which is explained hereafter, it is disclosed that a roughness on a surface can be improved by performing the thermal processing operation such as an RTA processing operation for 1 to 3000 seconds at a temperature 950° C. to 1150° C. in a hydrogen gas or an argon gas atmosphere.                Japanese Unexamined Patent Application, First Publication No. Hei 11-135514 (paragraph No. 0013, FIGS. 1 and 2) (Patent Document 1)        Japanese Unexamined Patent Application, First Publication No. 2000-91342 (paragraph No. 0009, FIGS. 2 and 3) (Patent Document 2)        
However, the RTA processing operation is performed at a relatively high temperature such as 950° C. or higher for improving a quality of a surface of the silicon single-crystal layer. If such a high temperature thermal processing operation is performed, it is inevitable such that a metal contamination is caused by a thermal processing device (furnace) which is used for the thermal processing operation.
Also, although a micro-roughness on a surface of the silicon single-crystal layer may be improved, a background (haze) level may be deteriorated for a reflected light which is measured by a particle counter when a surface condition is examined by a particle counter (a device for examining a surface condition optically according to a reflected light from a surface of an object which is supposed to be observed).
Furthermore, in a case in which the silicon single-crystal layer is a silicon wafer which is manufactured by modifying an ingot of the silicon single-crystal which is grown while being pulled up accordingn to the CZ method such that an oxygen precipitated nuclei is disposed therein, there are disadvantages in that the oxygen precipitated nuclei disappears in the silicon single-crystal layer by performing the thermal processing operation at such a high temperature; thus, a BMD density in the silicon single-crystal layer may be reduced greatly after the thermal processing operation for the device.
Also, conventionally, a lapping operation and an etching operation are performed for a silicon wafer which is cut from a silicon ingot a thermal processing operation. After that the silicon wafer is cleaned. Furthermore, a thermal processing operation (this thermal processing operation is called a donor killer thermal processing operation (DK thermal processing operation)) is performed to the silicon wafer for approximately 30 minutes at a temperature 600° C. to 800° C. in an inert atmosphere such as a nitrogen, etc., separately from the above high temperature operation such as the RTA processing operation in order to erase a thermal donor which is caused by an oxygen which exists in this silicon single-crystal layer. After that, a grinding operation is performed.
Hoever, in such a DK processing operation, there has been a case in which a life time and a diffusion length in a minority carrier may be reduced when a remaining metal contamination diffuses in the wafer in a cleaning step after the etching operation. Furthermore, the inventors of the present invention found a fact that there is a phenomenon in that a pit is evident and the GOI is deteriorated in a later step for forming a device when a quite a few incompletenesses which are caused by a modification remain on a surface of the silicon and a cleaning operation or an etching operation is performed by various chemicals such as HF, SC1 in a later grinding step.